Traveler's diarrhea (TD), sometimes tourist diarrhea or traveler's dysentery,[1] is a stomach and intestinal infection, and the most common illness affecting travelers.[2] It is defined as three or more unformed stools passed by a traveler within a 24-hour period. It is commonly accompanied by abdominal cramps, nausea, and bloating.[3] The diagnosis does not imply causative organism, but enterotoxigenic Escherichia coli (ETEC) is the most common pathogen.[4]Bacteria are responsible for roughly 80% of cases; most of the rest are caused by viruses and protozoans.

Although most travelers with TD recover within a few days with little or no treatment, symptoms can sometimes be severe enough to require medical intervention. In those who are immunocompromised or otherwise prone to serious infections, TD is a significant concern and occasionally even life-threatening.

An estimated 10 million people—20% to 50% of international travelers—develop TD each year.[5] It is more common in the developing world, where rates exceed 60%, but has been reported in some form in virtually every travel destination in the world.[6]

The onset of TD usually occurs within the first week of travel, but may occur at any time while traveling, and even after returning home, depending on the incubation period of the infectious agent. Bacterial TD typically begins abruptly, but Cryptosporidium may incubate for seven days, and Giardia for 14 days or more, before symptoms develop. Typically, a traveler experiences four to five loose or watery bowel movements each day. Other commonly associated symptoms are abdominal cramping, bloating, fever, and malaise.[5] Appetite often decreases significantly.[3]

Blood or mucus in the diarrhea, significant abdominal pain, or high fever suggests a more serious cause, such as cholera, characterized by a rapid onset of weakness and torrents of watery diarrhea with flecks of mucus (described as "rice water" stools). Dehydration is a serious consequence of cholera, and deaths have been reported as rapidly as 24 hours after onset.[3]

While viruses are associated with less than 20% of adult cases of traveler's diarrhea, they may be responsible for nearly 70% of cases in infants and children. Diarrhea due to viral agents is unaffected by antibiotic therapy, but is usually self-limited.[3] Protozoans such as Giardia lamblia and Cryptosporidium can also cause diarrhea. Pathogens commonly implicated in travelers' diarrhea appear in the table in this section.[3]

A sub-type of traveler's diarrhea afflicting hikers and campers, sometimes known as wilderness diarrhea, may have a somewhat different frequency of distribution of pathogens.[7]

The primary source of infection is ingestion of fecally-contaminated food or water. Attack rates are similar for men and women.[5]

The most important determinant of risk is the traveler's destination. High risk destinations include developing countries in Latin America, Africa, the Middle East, and Asia.[5] Among backpackers, additional risk factors include drinking untreated surface water and failure to maintain personal hygiene practices and clean cookware.[8] Campsites often have very primitive (if any) sanitation facilities, making them potentially as dangerous as any developing country.

Travelers often get diarrhea from eating and drinking foods and beverages that have no adverse effects on local residents. This is due to immunity that develops with constant, repeated exposure to pathogenic organisms. The extent and duration of exposure necessary to acquire immunity has not been determined; it may vary with each individual organism. A study among expatriates in Nepal suggests that immunity may take up to seven years to develop—presumably in adults who avoid deliberate pathogen exposure.[9] Conversely, immunity acquired by American students while living in Mexico disappeared, in one study, as quickly as eight weeks after cessation of exposure.[10]

Most published recommendations for prevention of TD include avoidance of questionable foods or beverages, based on the assumption that TD is fundamentally a sanitation failure, leading to bacterial contamination of drinking water and food.[5] The efficiency of this method has been questioned, given the lack of travelers' control over sanitation in hotels and restaurants, and the paucity of evidence of a correlation between scrupulous food vigilance and a decrease in the risk of acquiring TD.[11] Nevertheless, travel medicine guidelines continue to recommend that travelers take basic precautions when making food and beverage choices:

Maintain good hygiene and use only safe water for drinking and tooth brushing.[3]

Safe beverages include bottled water, bottled carbonated beverages, hot tea or coffee, and water boiled or appropriately treated by the traveler.[3] Caution should be exercised with hot beverages, which may be only heated, not boiled.[5]

In restaurants, insist that bottled water be unsealed in your presence. Reports of locals filling empty bottles with untreated tap water and reselling them as "purified" water have surfaced.[3] When in doubt, a bottled carbonated beverage is the safest choice, since it is difficult to simulate carbonation when refilling a used bottle.

Avoid green salads, because it is unlikely that the lettuce will have been washed with safe water.[5]

If handled properly, well-cooked and packaged foods are usually safe.[5] Raw or undercooked meat and seafood should be avoided. Unpasteurized milk, dairy products, mayonnaise and pastry icing are associated with increased risk for TD, as are foods or drinking beverages purchased from street vendors or other establishments where unhygienic conditions may be present.[3]

Although safe bottled water is widely available in all but the most remote destinations, travelers can treat their own water if necessary, or as an extra precaution.[3] Techniques include boiling, filtering, chemical treatment, and ultraviolet light. Boiling kills all active bacteria and viruses immediately. (Prolonged boiling is unnecessary; microorganisms are killed within seconds as water temperature passes 55–70 degrees C (130-160 degrees F).[12]) Prions and some bacterial and fungal spores may require a longer period (15 or more minutes) of boiling for complete inactivation.[13] Filters eliminate most bacteria and protozoa, but not viruses. Chemical treatment with halogens — chlorine bleach (2 drops per litre), tincture of iodine (5 drops per litre), or commercial tablets — are not effective against protozoa such as Giardia. An ultraviolet (UV) water purification device is available commercially that allows treatment of small amounts of water at room temperature. The UV light bonds DNA thymine rings, preventing the survival or replication of any infectious organisms in the water. It kills both viruses and cellular organisms. Other claimed advantages include no taste alteration, elimination of the need for boiling, and decreased long-term cost compared with bottled water.

Several studies show that oral bismuth subsalicylate (two tablets or two fluid ounces four times daily) reduces the incidence of TD,[3][14][15] although many travelers find a four-times-per-day regimen inconvenient.[16] Potential side effects include black tongue, black stools, nausea, constipation, and ringing in the ears (tinnitus). Bismuth subsalicylate should not be taken by those with aspirin allergy, kidney disease, or gout, nor concurrently with certain antibiotics such as the quinolones, and should not be taken continuously for more than three weeks.[16]

An oral formulation of hyperimmune bovine colostrum is marketed by an Australian manufacturer for prevention of ETEC-induced TD. While hyperimmune colostrum demonstrated no theoretical advantage over natural colostrum in neutralizing 19 common human pathogens (including E. coli) in one study,[17] the Australian product (one tablet three times daily) has shown efficacy in preventing TD symptoms after artificial challenge with a homologous laboratory strain of ETEC in one company-sponsored controlled trial.[18] As yet, there are no published studies of efficacy under actual travel conditions.

Though effective, antibiotics are not recommended for prevention of TD in most situations, because of the risk of allergy or adverse reactions to the antibiotics, and because intake of prophylactic antibiotics may decrease effectiveness of such drugs should a serious infection occur. Antibiotics can also cause vaginal yeast infections (which many women consider a worse problem than diarrhea[16]), or overgrowth of the bacterium Clostridium difficile, leading to pseudomembranous colitis and its associated severe, unrelenting diarrhea.[19]

Antibiotic prophylaxis may be warranted in special situations where benefits outweigh the above risks, such as immunocompromised travelers, chronic intestinal disorders, prior history of repeated disabling bouts of TD, or scenarios in which the onset of diarrhea might prove particularly troublesome. Options for prophylactic treatment include the quinolone antibiotics (norfloxacin, ciprofloxacin, ofloxacin, among others), azithromycin, and trimethoprim/sulfamethoxazole, though the latter has proved less effective in recent years.[16][20] Quinolone antibiotics may bind to metallic cations such as bismuth, and should not be taken concurrently with bismuth subsalicylate. Trimethoprim/sulfamethoxazole should not be taken by anyone with a history of sulfa allergy.[16] As with any medication, the risk of allergies and potential adverse side effects must always be considered.

A number of pathogen-specific vaccines are available or under development. A monovalent inactivated oral vaccine against Vibrio cholerae has demonstrated a protective effect against TD in some patients when one dose is given a few weeks before travel and a second dose one week before travel, although the product is not specifically approved for that indication in most countries,[21] and a 2013 literature review found insufficient evidence to support its use against ETEC-induced TD.[22] Several vaccine candidates targeting ETEC or Shigella are in various stages of development.[23][24]

Two probiotics (Saccharomyces boulardii and a mixture of Lactobacillus acidophilus and Bifidobacterium bifidum) have been studied as a treatment for TD. In a meta-analysis by McFarland (2005), no serious adverse reactions were reported in 12 trials. These probiotics may offer a safe and effective method to prevent TD, but due to strain stability and survivability issues, they may not always be an appropriate choice.[25]Prebiotics, as an alternative, are more stable than probiotics during passage through the upper gastrointestinal tract and are able to induce antimicrobial effects principally through their selective stimulation of our own beneficial gut bacteria. However, prebiotics act mainly in the large intestine, while the infective organisms causing TD act in the small intestine. Therefore, current prebiotics (such as fructooligosaccharide) have very limited application as preventative agents. Second generation prebiotic galactooligosaccharides, such as B-GOS (Bimuno), have additional properties such as positive effect on immunity[26] and direct interaction with the host gut epithelium, preventing the attachment and invasion of gastrointestinal pathogens.[27] B-GOS was shown to result in significant reduction in the incidence and duration of TD in a study with human volunteers travelling to countries with medium to high risk of developing TD.[28]

Most cases of TD are mild and resolve in a few days without treatment; but severe or protracted cases may result in significant fluid loss and dangerous electrolytic imbalance. Dehydration due to diarrhea can also alter the effectiveness of medicinal and contraceptive drugs. Adequate fluid intake (oral rehydration therapy) is therefore a high priority. Commercial rehydration drinks[29] are widely available; alternatively, purified water or other clear liquids are recommended, along with salty crackers or oral rehydration salts (available in stores and pharmacies in most countries) to replenish lost electrolytes.[5] Carbonated water or soda, left open to allow dissipation of the carbonation, is useful when nothing else is available.[3] In severe or protracted cases, the oversight of a medical professional is advised.

If diarrhea becomes severe (typically defined as three or more loose stools in an eight-hour period), especially if associated with nausea, vomiting, abdominal cramps, fever, or blood in stools, medical treatment should be sought. Such patients may benefit from antimicrobial therapy.[5] A 2000 literature review found that antibiotic treatment shortens the duration and severity of TD; most reported side effects were minor, or resolved on stopping the antibiotic.[30]

Currently, the fluoroquinolone antibiotics are the drugs of choice. Trimethoprim-sulfamethoxazole and doxycycline are no longer recommended because of high levels of resistance to these agents.[5] Antibiotics are typically given for three to five days, but single doses of azithromycin or levofloxacin have been used.[31] If diarrhea persists despite therapy, travelers should be evaluated for possible viral or parasitic infections,[5] bacterial or amoebic dysentery, Giardia, helminths, or cholera.[3]

Antimotility drugs such as loperamide and diphenoxylate reduce the symptoms of diarrhea by slowing transit time in the gut. They may be taken to slow the frequency of stools, but not enough to stop bowel movements completely, which delays expulsion of the causative organisms from the intestines.[5] They should be avoided in patients with fever, bloody diarrhea, and possible inflammatory diarrhea.[32] Adverse reactions may include nausea, vomiting, abdominal pain, hives or rash, and loss of appetite.[33] Antimotility agents should not, as a rule, be taken for protracted periods, or by children under age two.[16]

There are a number of colloquialisms for travelers' diarrhea contracted in various localities, such as "Montezuma's revenge", "turistas",[34] or "Aztec two step" in Mexico; and "Pharaoh's Revenge," "mummy's tummy," or "Cairo two-step" in Egypt. Many other colorful synonyms exist in other regions of the world, some of which have found their way into the arts and literature. For example, Aamir Khan titled his 2011 Hindi filmDelhi Belly, after the popular Indian colloquialism.

Wilderness diarrhea (WD), also called wilderness-acquired diarrhea (WAD) or backcountry diarrhea, refers to diarrhea among backpackers, hikers, campers and other outdoor recreationalists in wilderness or "backcountry" situations, either at home or abroad.[7] It is caused by the same fecal microorganisms as other forms of traveler's diarrhea, usually bacterial or viral. Since wilderness campsites seldom provide access to sanitation facilities, the infection risk is similar to that of any developing country.[8] Water treatment, good hygiene and dish washing have all been shown to reduce the incidence of WAD.[36][37]